This application claims priority from Italian Patent Application TO2000A 000663 titled xe2x80x9cMetodo e Macchina di Molatura per la Lavorazione di Lastre di Vetro,xe2x80x9d filed Jun. 30, 2000; the contents of which is incorporated by reference herein in its entirety.
As is known, after the operations of etching and shearing have been carried out, semi-finished sheets of glass are obtained, the perimeter edges of which are in many cases ground in a grinding system, until the required final geometry is obtained.
In general, in the grinding systems used, the sheets are conveyed along a horizontal path of advance in the shape of an xe2x80x9cLxe2x80x9d, comprising a first and a second section which are at right-angles to one another, on each of which a work station is provided. Each sheet to be processed is advanced through the first work station, it is ground along two sides of the edge, which are disposed on opposite sides of the path of advance, it is moved away from the first station, and is translated towards the second work station, where the sheet is finally ground along the two sides of the edge which are transverse relative to the edges already ground.
The finished products obtained by means of the known grinding systems of the above-described type have the disadvantage that they do not have an invariable quality index relative to one another.
This is owing to the fact that, in order to grind the sides of the edge which are transverse relative to one another, it is necessary to carry out operations of squaring of the sheets at each of the two work stations, and to displace the sheets between the work stations themselves. The displacement from the first to the second work station, and the subsequent squaring in the second work station, give rise to inevitable errors of positioning, which detract from perfect success of the grinding.
In addition, the grinding cycle has relatively lengthy unproductive times, caused substantially by the displacement of the sheets of glass between the two work stations.
Also, as a result of the errors of positioning at the two work stations, the grinding tools reach their limit condition of wear in periods of time which a priori are unforeseeable, and are sometimes extremely short, such that their maintenance and replacement is difficult to plan.
In addition, the known grinding systems of the above-described type have relatively large sizes, owing substantially to the presence of the two work stations, which are disposed along a path in the shape of an xe2x80x9cLxe2x80x9d, and above all have a low level of flexibility, and are designed to process batches of sheets which all have the same dimensions, since the machining position of the grinding wheels cannot be adapted on the basis of the dimensions of each sheet to be processed, except by means of particularly lengthy setting times.
Japanese patent application JP 08 197 402 discloses a grinding machine in which the edge of a sheet of glass is ground in a single work station. For this type of machine there is a known need to grind sheets of glass of varying dimensions and geometries, particularly in such a way as to avoid interference between the grinding wheels and the glass supporting, positioning and retention members.
The object of the present invention is to provide a grinding machine for machining sheets of glass, which makes it possible to solve the above-described problems simply and economically.
The present invention provides a grinding machine for machining sheets of glass having respective peripheral edges that at least partly require grinding. The machine comprises a support structure, a single work station accommodating positioning means for arranging the sheet of glass in an unambiguous reference position on a horizontal plane with respect to the support structure, retention means for retaining the sheet of glass in the reference position during grinding, and motorized grinding means for grinding the peripheral edge in the work station. The machine also comprises actuator means for vertically displacing the retention means between a raised position for machining the sheet of glass and a lowered rest position.